Biodegradable polyester resin composition, process for producing the same and formed article and molded and molded article using the same

ABSTRACT

It is intended to provide a biodegradable polyester resin composition which is excellent in gas barrier properties, mechanical strength and heat resistance and has Theological characteristics advantageously usable in molding a foamed article, etc., a process for producing the same, and a foamed article and a molded article using the same. The biodegradable polyester resin composition contains 100 parts by mass of a biodegradable polyester resin containing 59% mole or more of a hydroxycarboxylic acid unit, 0.01 to 10 parts by mass of a (meth)acrylic acid ester compound and 0.05 to 20 parts by mass of a layered silicate.

TECHNICAL FIELD

The present invention relates to a biodegradable polyester resincomposition excellent in mechanical strength and heat resistance,causing no trouble in operation, having rheological characteristicsadvantageously usable in molding of a foamed article or a moldedarticle, and excellent in gas barrier properties, and a process forproducing the same and a foamed article and a molded article using thesame.

BACKGROUND ART

Polylactic acid has a feature that it has a higher melting point and issuperior in heat resistance compared to other biodegradable resins.However, since polylactic acid has a low melt viscosity, there areproblems, for example, that a sufficient expansion ratio cannot beachieved because bubbles are broken upon extrusion foaming and that thethickness of molded articles tends to be uneven because bubbles are notstable in inflation molding or blow molding. Thus, molding conditionsare severely restricted. Further, due to its low crystallization rate,polylactic acid has a disadvantage of low production efficiency ininjection molding and the like. Therefore, for practical use, it isnecessary to improve the melt viscosity, make effective the strainhardening property when measuring elongational viscosity, and to improvethe crystallization rate.

Generally, to impart strain hardening properties to a resin composition,a method of adding a polymer of a high polymerization degree or a methodof using a polymer containing a long branched chain is considered to beeffective. However, in the production of a polymer of a highpolymerization degree, polymerization takes a long time, and not onlyproduction efficiency is lowered but also coloring or decomposition dueto long thermal history is found. For this reason, biodegradablepolyester having a weight average molecular weight of, for example,500,000 or higher, has not been practically used. On the other hand, asthe method of producing polylactic acid containing a long branchedchain, a method comprising adding a polyfunctional initiator forpolymerization is known (JP-A-10-7778, JP-A-2000-136256). However,introduction of branched chain during polymerization involves a problemthat discharge of resin is difficult and the degree of branching cannotbe arbitrarily modified. Further, methods comprising melt-kneading alayered silicate have also been studied. JP-A-2001-89646 discloses thata resin with a high rigidity and an increased biodegradation rate can beobtained by melt-kneading with a resin a layered clay mineral that hasbeen organized and made to have an average particle size of not morethan 1 μm. However, the publication does not contain concretedescription of how to adjust the average particle size of the layeredclay mineral to not more than 1 μm, and it completely lacks descriptionof molding conditions, and thus whether the moldability was improved ornot is unknown.

On the other hand, a method comprising preparing a biodegradable resinand then melt-kneading the same with a peroxide or a reactive compoundto be crosslinked, thereby yielding a strain hardening property. Thismethod is variously studied because it is simple and branching can bearbitrarily modified. However, acid anhydride and polycarboxylic acidused in JP-A-11-60928 are not practical because the reactivity tends tobe unstable and the pressure must be reduced. In addition, in the caseof polyisocyanate used in JP-B-2571329 and JP-A-2000-17037, itsmolecular weight tends to be decreased upon melting and this causessafety problems in operation. Thus, technology satisfying practicalrequirements has not yet been established.

JP-A-10-324766 discloses that foaming can be effectively performed whena biodegradable polyester resin synthesized from dibasic acid and glycolis combined and crosslinked with an organic peroxide and a compoundcontaining an unsaturated bond. This method is an example of immersingthese crosslinking agents to resin fine particles at a temperature lowerthan the melting point of the resin, and the case in whichdivinylbenzene is used as a coagent is described in detail. However, useof (meth)acrylic acid ester compound is not studied, and onlyapplication to a biodegradable polyester resin synthesized from dibasicacid and glycol having a low heat resistance has been studied. Further,regarding addition of these crosslinking agent and coagent, no techniquefor stable and long term operation has been suggested.

A biodegradable polyester with improved heat resistance composed mainlyof α- and/or β-hydroxycarboxylic acid unit is also known. However, thisbiodegradable polyester has a low crystallization rate and is poor inoperation ability in molding such as injection molding. To solve thisproblem, a method of adding inorganic powder has been suggested, but itis not satisfactory.

In addition, gas barrier properties, in particular oxygen barrierproperty of biodegradable polyester is insufficient, and it wasimpossible to use biodegradable polyester for applications requiring gasbarrier properties, such as food containers. To improve gas barrierproperties, a method of dispersing a layered silicate in a resin hasbeen proposed. It is considered that the gas barrier property isimproved because permeation of the gas component is blocked by thelayered silicate in the resin and the gas moves around the layeredsilicate. For example, usefulness of layered silicate in polyamide resinis disclosed in JP-B-3284552 and application of layered silicate toaliphatic polyester is disclosed in JP-A-2001-164097. However,rheological characteristics suitable for various molding processescannot be achieved only by mixing a layered silicate to a resin, andthere is a problem of poor operation ability.

The present invention solves the above described problems and provides abiodegradable polyester resin composition excellent in mechanicalstrength and heat resistance, having a high crystallization rate,causing no trouble in operation, having rheological characteristicsadvantageously usable in molding of a foamed article or a moldedarticle, and excellent in gas barrier properties, and a process forproducing the same and a foamed article and a molded article using thesame.

DISCLOSURE OF THE INVENTION

The present inventors have conducted intensive studies and as a resultcompleted the present invention. Accordingly, the present inventionrelates to a biodegradable polyester resin composition comprising 100parts by mass of a biodegradable polyester resin containing not lessthan 50% by mole of an α- and/or β-hydroxycarboxylic acid unit,, 0.01 to10 parts by mass of a (meth)acrylic acid ester compound and 0.05 to 20parts by mass of a layered silicate.

The present invention also relates to a process for producing abiodegradable polyester resin composition which comprises melt-kneadinga biodegradable polyester resin with a layered silicate and then addinga (meth) acrylic acid ester compound and a peroxide thereto, or pouringa solution or a dispersion of a (meth) acrylic acid ester compound, or asolution or a dispersion of a (meth)acrylic acid ester compound and aperoxide, followed by melt-kneading.

The present invention also relates a biodegradable resin foamed articleobtained by foam molding of a biodegradable polyester resin compositionof the present invention.

The present invention also relates a biodegradable resin molded articleobtained by any of injection molding, extrusion molding and blow moldingof a biodegradable polyester resin composition of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the relationship between elongation time[s] and elongational viscosity [Pa·s] for determining a modulus ofstrain hardening (a₂/a₁). Note that a₁, is a gradient in a linear regionat an initial stage of elongation before appearance of a bending point Mand a₂ is a gradient of a later stage of elongation after the bendingpoint M.

FIG. 2 is a graph illustrating the relationship between crystallizationdegree (θ) and time (minutes) for determining a crystallization rateindex. The crystallization rate index represents the time for reachingthe half of the crystallization degree finally reached.

BEST MODE FOR CARRYING OUT THE INVENTION

The biodegradable polyester resin composition of the present inventionis essentially a specific compound containing a biodegradable polyesterresin, a (meth)acrylic acid ester compound and a layered silicate. Bymixing a (meth)acrylic acid ester compound with a biodegradablepolyester resin excellent in heat resistance, the crystallization ratebecomes higher and the moldability is improved.

However, by simply mixing a (meth)acrylic acid ester compound, therigidity at higher temperature is low and sufficient operationabilitycannot be obtained. Thus, in the present invention, by mixing a layeredsilicate in addition to a (meth)acrylic acid ester compound, a resincomposition can be produced, whose rigidity at higher temperature hasbeen improved by further increasing the melt viscosity and exerting thestrain hardening property in an elongational viscosity measurement, andwhich is excellent in operationability and has rheologicalcharacteristics advantageously usable in molding of a foamed article.Further, by mixing a layered silicate, heat resistance can be furtherimproved and mechanical properties and dimensional stability can befurther improved, and in addition, gas barrier properties, inparticular, oxygen barrier properties, are improved.

The biodegradable polyester resin composition of the present inventionconfigured as above has a high melt viscosity, is excellent in strainhardening property when measuring elongational viscosity and has a highcrystallization rate. However, these advantages cannot be obtained onlyby mixing a biodegradable polyester resin, a (meth)acrylic acid estercompound and a layered silicate. In the present invention, problems inoperation can be solved by producing the biodegradable polyester resincomposition configured as above by the production process of the presentinvention, and the obtained molded article is excellent in heatresistance and mechanical strength and has good appearance.

The present invention will now be described in detail below.

The biodegradable polyester resin composition of the present inventionneeds to contain 100 parts by mass of a biodegradable polyester resincontaining not less than 50% by mole of an α- and/or β-hydroxycarboxylicacid unit, 0.01 to 10 parts by mass of a (meth)acrylic acid estercompound and 0.05 to 20 parts by mass of a layered silicate.

The biodegradable polyester resin which is the main component needs tocontain not less than 50% by mole of an α- and/or β-hydroxycarboxylicacid unit. When the content of the α- and/or β-hydroxycarboxylic acidunit is less than 50% by mole, biodegradability and heat resistance aredecreased.

Examples of α- and/or β-hydroxycarboxylic acid units include D-lacticacid,-L-lactic acid or a mixture thereof, glycolic acid,3-hydroxybutyric acid, 3-hydroxyvaleric acid and 3-hydroxycaproic acid.In particular, biodegradable polyester resins containing D-lactic acid,L-lactic acid or a mixture thereof are preferred because they areexcellent in mechanical strength and heat resistance. In the presentinvention, the resin composition preferably contains not less than 50%by mole of polylactic acid, polyglycolic acid, poly(3-hydroxybutyricacid), poly(3-hydroxyvaleric acid), poly(3-hydroxycaproicacid), or acopolymer or mixture thereof.

The biodegradable polyester resin in the present invention may beproduced by generally known melt polymerization or by further usingsolid state polymerization together. Poly(3-hydroxybutyric acid),poly(3-hydroxyvaleric acid) and the like may also be produced using amicroorganism.

In the biodegradable polyester resin in the present invention, anotherbiodegradable resin may be copolymerized or mixed therewith if necessarywithin the limit that the heat resistance of poly(α- and/orβ-hydroxycarboxylic acid) is not significantly damaged. Examples ofother biodegradable resins include aliphatic polyesters composed of dioland dicarboxylic acid which are typically poly(ethylene succinate) andpoly(butylene succinate), poly(ω-hydroxyalkanoates) which are typicallypoly(□-caprolactone), (butylene succinate-butyleneterephthalate)copolymers and (butylene adipate-butyleneterephthalate)copolymers which are biodegradable despite that theycontain an aromatic component, polyester amides, polyester carbonatesand polysaccharides such as starch.

Though the molecular weight of the biodegradable polyester resin in thepresent invention is not particular limited, the resin has a weightaverage molecular weight of preferably 50,000 to 1,000,000, morepreferably 100,000 to 1,000,000. A weight average molecular weight ofless than 50,000 is not preferable because the melt viscosity of theresin composition becomes too low. A weight average molecular weight ofmore than 1,000,000 is not preferable because moldability of the resincomposition is suddenly reduced.

As the (meth) acrylic acid ester compound in the present invention,compounds containing at least two (meth)acrylic groups or at least one(meth)acrylic group and at least one glycidyl group or vinyl group arepreferred, because they are highly reactive to the biodegradable resinand thus monomer hardly remains, and they are relatively less toxic andcause little coloring of the resin. Specific examples of such compoundsinclude glycidyl methacrylate, glycidyl acrylate, glyceroldimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropanetriacrylate, allyloxypolyethylene glycol monoacrylate,allyloxypolyethylene glycol monomethacrylate, polyethylene glycoldimethacrylate, polyethylene glycol diacrylate, polypropylene glycoldimethacrylate, polypropylene glycol diacrylate and polytetramethyleneglycol dimethacrylate. Additional examples thereof include copolymersthereof containing various lengths of those alkylene glycol moieties,butanediol methacrylate and butanediol acrylate.

The mixing ratio of the (meth)acrylic acid ester compound in the presentinvention needs to be 0.01 to 10 parts by mass, preferably 0.05 to 5parts by mass based on 100 parts by mass of the biodegradable polyesterresin. When the mixing ratio of the (meth)acrylic acid ester compound isless than 0.01 parts by mass, the effect of improving mechanicalstrength, heat resistance and dimensional stability which is an objectof the present invention cannot be obtained. When the mixing ratio ofthe (meth)acrylic acid ester compound is more than 10 parts by mass, thecrosslinking degree is too high and the operation ability is poor.

In the present invention, concurrent use of peroxide when mixing the(meth)acrylic acid ester compound with the biodegradable polyester resinis preferable because the crosslinking reaction is accelerated and thestrain hardening property is easily exerted. Examples of peroxidesinclude benzoyl peroxide, bis(butylperoxy)trimethylcyclohexane,bis(butylperoxy)cyclododecane, butylbis (butylperoxy)valerate, dicumylperoxide, butylperoxybenzoate, dibutyl peroxide,bis(butylperoxy)diisopropylbenzene, dimethyldi(butylperoxy)hexane,dimethyldi(butylperoxy) hexyne and butylperoxycumene.

The mixing ratio of peroxide is preferably 0.02 to 20 parts by mass,more preferably 0.05 to 10 parts by mass based on 100 parts by mass ofthe biodegradable polyester resin. The peroxide may be mixed at a mixingratio of more than 20 parts by mass, but it is disadvantageous in termsof the cost. Since peroxide decomposes when mixed with the resin, theobtained resin composition may not contain peroxide even if it is usedwhen mixing.

The mixing ratio of the layered silicate in the present invention needsto be 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass basedon 100 parts by mass of the biodegradable polyester resin. When themixing ratio of the layered silicate is less than 0.05 parts by mass,sufficient mechanical strength and heat resistance cannot be obtained.When the mixing ratio is more than 20 parts bymass, the obtainedcomposition may be brittle and there is disadvantage in terms of thecost. In addition, although gas barrier properties are improved bymixing the layered silicate, this advantage is substantially the sameeven if more than 20 parts by mass of the layered silicate is mixed.

Specific examples of layered silicate include smectite, vermiculite andswellable fluoromica. Examples of smectites include montmorillonite,beidellite, hectorite and saponite. Examples of swellable fluoromicasinclude Na-type tetrasilisic fluoromica, Na taeniolite and Litaeniolite. In addition to those described above, layered silicatescontaining no aluminum or magnesium such as kanemite, makatite,magadiite and kenyte may also be used. Of these, layered silicateshaving a high aspect ratio, such as montmorillonite and swellablefluoromica, are preferred, and swellable fluoromica is particularlypreferred, in order to improve gas barrier properties. Further, thelayered silicate may be a natural product or a synthetic product. Themethod of producing synthetic layered silicate may be any of fusion,intercalation , hydrothermal synthesis, etc. These layered silicates maybe used alone or in a combination of two or more of minerals withdifferent kinds, origins, production methods, particle sizes, etc.

It is preferable that the layered silicate in the present invention ispreviously treated by an organic cation. Examples of organic cationsinclude ammonium ions generated by protonation of primary to tertiaryamines, quaternary ammonium ions and onium ions such as phosphonium ion.Examples of primary amines include octylamine, dodecylamine andoctadecylamine. Examples of secondary amines include dioctylamine,methyloctadecylamine and dioctadecylamine. Examples of tertiary aminesinclude trioctylamine, dimethyldodecylamine anddidodecylmonomethylamine. Examples of quaternary ammonium ions includetetraethylammonium, octadecyltrimethylammonium,dimethyldioctadecylammonium, dihydroxyethylmethyloctadecylammonium,methyldodecylbis (polyethylene glycol)ammonium andmethyldiethyl(polypropylene glycol)ammonium. Examples of phosphoniumions include tetraethylphosphonium, tetrabutylphosphonium,hexadecyltributylphosphonium, tetrakis(hydroxymethyl)phosphonium and2-hydroxyethyltriphenylphosphonium. Of these,dihydroxylethylmethyloctadecylammonium, methyldodecylbis (polyethyleneglycol)ammonium, methyldiethyl(polypropylene glycol) ammonium and oniumions having 1 or more hydroxyl groups in the molecule such as2-hydroxyethyltriphenylphosphonium are particularly preferred becauselayered silicates treated with these have high compatibility withpolyester resin, especially biodegradable polyester resin and becausethe dispersibility of such layered silicates is increased. These organiccations may be used alone or in combination of two or more kinds.

Examples of methods of treating layered silicate with theabove-described organic cation include a method comprising dispersing alayered silicate in water or alcohol, then adding a salt of theabove-described organic cation followed by mixing with stirring, therebyperforming ion exchange of the inorganic ion of the layered silicatewith the organic cation, then filtrating, washing and drying.

A compatibilizer may also be used with layered silicate so as to improvedispersibility in polyester resin. The compatibilizer is added in anamount of preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5parts by mass based on 100 parts by mass of the biodegradable polyesterresin. When the mixing ratio of the compatibilizer is more than 10 partsby mass, heat resistance and mechanical strengths of the biodegradablepolyester resin composition may be decreased. As the compatibilizer,compounds compatible with both polyester resin, especially biodegradablepolyester resin, and layered silicate, such as polyalkylene oxides,aliphatic polyesters, polyhydric alcohol esters and polycarboxylic acidesters are used. Examples of polyalkylene oxides include polyethyleneglycol, polypropylene glycol, polybutylene glycol and copolymersthereof. At least one of the terminal hydroxyl groups may be blocked byan alkoxy group, or esterified by monocarboxylic acid or dicarboxylicacid. Examples of aliphatic polyesters include polyhydroxycarboxylicacids such as polylactic acid, polyglycolic acid, poly(3-hydroxybutyricacid), poly(3-hydroxyvaleric acid) and poly(3-hydroxycaproic acid),poly(ω-hydroxyalkanoates) which are typically poly(ε-caprolactone)andpoly(δ-valerolactone), and aliphatic polyesters composed of diol anddicarboxylic acid which are typically poly(ethylene succinate),poly(butylene succinate) and (butylene succinate-butyleneadipate)copolymers. A terminal carboxyl group of these aliphaticpolyesters may be esterified by alcohol or substituted by a hydroxylgroup of diol. Examples of polyhydric alcohol esters include glycerolesters such as monoglyceride, diglyceride and triglyceride which areesters of glycerol and aliphatic acid, and pentaerythritol esters.Examples of polycarboxylic acid esters include citrates such as tributylcitrate and tributyl citrate acetate.

The above-described compatibilizer preferably has a boiling point of notlower than 250° C. When the boiling point is lower than 250° C., gas maybe generated during molding and bleed-out from molded article may occur.The compatibilizer preferably has a number average molecular weight ofpreferably 200 to 50,000, more preferably 500 to 20,000. When the numberaverage molecular weight is less than 200, gas is easily generatedduring molding and bleed-out from molded article tends to occur, and themechanical strength and the heat resistance of the molded article may bedecreased. When the number average molecular weight is higher than50,000, the effect of improving dispersibility of layered silicate tendsto decrease.

Examples of methods of adding compatibilizer include a method in whichthe above-described compound is previously impregnated into layeredsilicate directly, a method comprising mixing the above-describedcompound in the presence of water or an organic solvent and thenremoving water or the organic solvent by filtration or the like, amethod of adding a compatibilizer when melt-kneading polyester resin andlayered silicate and a method of adding compatibilizer together withlayered silicate when synthesizing polyester resin. Preferably used is amethod in which a compatibilizer is mixed with layered silicate beforemixing with polyester.

Preferred states of dispersion of layered silicate in the biodegradablepolyester resin in the present invention include complete exfoliationtypes in which layered silicate is exfoliated into individual platelets,intercalation types in which resin molecules are inserted in betweenlayers, and combinations of these. In a quantitative view, the averagethickness of the single layer or the stacked layers of layered silicateis preferably 1 to 100 nm, more preferably 1 to 50 nm, and furtherpreferably 1 to 20 nm as measured by a transmission electron microscope;or the interlayer distance as measured by X-ray diffraction ispreferably not less than 2.5 nm, more preferably not less than 3 nm,further preferably not less than 4 nm, and most preferably no peakattributable to the interlayer distance being observed. Examples ofmethods of controlling dispersibility of such layered silicate include,in a kneading method, modification of kneading conditions, use of theabove-described compatibilizer and introduction of a polar group intothe resin. Generally, when layered silicate is added upon polymerizationof polyester, dispersibility can be further increased to improve gasbarrier properties.

The biodegradable polyester resin composition of the present inventionhas a modulus of strain hardening of preferably not less than 1.05to notmore than 50, more preferably 1.5 to 30. When the modulus of strainhardening is less than 1.05, bubbles are broken upon extrusion foaming,and the thickness of molded articles tends to be uneven. When themodulus of strain hardening is more than 50, gel is easily generatedupon molding and flowability is significantly decreased, and so thisrange is not preferable. As shown in FIG. 1, the modulus of strainhardening refers to the ratio (a₂/a₁) of a gradient a₁, in a linearregion at an initial stage of elongation before appearance of a bendingpoint M to a gradient a₂ of a later stage of elongation after thebending point M in a logarithmic plot of time-elongational viscosityobtained by measuring elongational viscosities at a temperature 10° C.higher than the melting point.

The biodegradable polyester resin composition of the present inventionhas a crystallization rate index of preferably not more than 30(minutes). The smaller the crystallization rate index, the higher thecrystallization rate, and the larger the crystallization rate index, thelower the crystallization rate. As shown in FIG. 2, the crystallizationrate index is the time (minutes) for reaching the half of thecrystallization degree (θ) finally reached when a resin is once meltedat 200° C. using a DSC instrument and crystallized isothermally at 130°C. When the crystallization rate index is higher than 30 (minutes),crystallization takes too long, molded articles of desired shapes cannotbe obtained and the cycle time in injection molding is prolonged toreduce productivity. Further, because too high a crystallization ratereduces moldability, the lower limit of the crystallization rate indexis preferably about 0.1 (minutes). The larger the amount of crosslinkingagent and/or peroxide, the smaller the crystallization rate index, thehigher the crystallization rate can be. The crystallization rate isfurther increased by adding 0.05 part by mass or more of layeredsilicate. When 0.1 to 5% by mass of inorganic powder such as talc orcalcium carbonate is added, the crystallization rate is furtherincreased by the synergistic effect. The greater the number offunctional groups of the crosslinking agent, the higher thecrystallization rate.

The biodegradable polyester resin composition of the present inventionmay be produced by mixing a biodegradable polyester resin, a(meth)acrylic acid ester compound and a layered silicate at a mixingratio defined in the present invention, and melt-kneading the same usinga general extruder. However, it is difficult to promote a crosslinkingreaction and achieve strain hardening property by simple melt-kneadingof these. Thus, when producing a biodegradable polyester resincomposition in the present invention, peroxide is used, or a solution ora dispersion of a (meth)acrylic acid ester compound is used, and at thesame time, a biodegradable polyester resin and a layered silicate arepreviously melt-kneaded.

The approach will be described in detail below.

In the method of producing a biodegradable polyester resin compositionof the present invention, first a biodegradable polyester resin and alayered silicate are introduced into an inlet of a kneader bydry-blending or using a volumetric feeder or the like and kneaded.

Then, a (meth)acrylic acid ester compound is introduced from the middleof the kneader to melt-knead the materials, and at this time, peroxideis preferably used together. Peroxide is supplied using a powder feederwhen it is solid or by a pressure pump when it is liquid. Alternatively,a solution or a dispersion of a (meth)acrylic acid ester compound may bepoured.

In the present invention, it is desirable to dissolve or disperse the(meth)acrylic acid ester compound and/or peroxide in a medium and pourit into the kneader because operation ability is significantly improved.Specifically, it is preferable that a solution or a dispersion of the(meth)acrylic acid ester compound is poured thereinto when melt-kneadingthe biodegradable polyester resin and the peroxide, or a solution or adispersion of the (meth)acrylic acid ester compound and the peroxide ispoured and melt-kneaded when melt-kneading the biodegradable polyesterresin.

As the medium for dissolving or dispersing the (meth)acrylic acid estercompound and/or peroxide, a usual medium may be used without anylimitation, and plasticizers excellent in compatibility with thealiphatic polyester in the present invention are preferred, and thosebiodegradable are preferred. The medium may be, for example, at leastone plasticizer selected from aliphatic polycarboxylic acid esterderivatives, aliphatic polyhydric alcohol ester derivatives, aliphaticoxyester derivatives, aliphatic polyether derivatives and aliphaticpolyether polycarboxylic acid ester derivatives. Specific examples ofsuch compound include dimethyl adipate, dibutyl adipate, triethyleneglycol diacetate, methyl acetyl ricinoleate, tributyl acetylcitrate,polyethylene glycol and dibutyl diglycol succinate. The plasticizer isused in an amount of preferably not more than 30 parts by mass, morepreferably 0.1 to 20 parts by mass based on 100 parts by mass of theresin. The plasticizer need not be used when the crosslinking agent haslow reactivity, but when it has high reactivity, 0.1 part by mass ormore of a plasticizer is preferably used. The (meth)acrylic acid estercompound and the peroxide may be added separately.

For a better kneading condition, a twin screw extruder may be used. Thekneading temperature is in the range of preferably (melting point ofresin +5C.) to (melting point of resin +100° C.), and the kneading timeis preferably 20 seconds to 30 minutes. When the temperature and thetime are below the range, kneading and reaction are insufficient. Whenthe temperature and the time are above the range, the resin may bedecomposed or colored.

The biodegradable polyester resin composition of the present inventionmay be produced by melt-kneading a biodegradable polyester resin, a(meth)acrylic acid ester compound, a peroxide and a layered silicate asraw materials as described above. Because peroxide is generallydecomposed during melt-kneading, the obtained resin composition does notnecessarily contain peroxide. In addition, a medium such as plasticizeris preferably used upon addition of a (meth)acrylic acid ester compoundand/or peroxide, but this medium may also evaporate upon melt-kneading,and thus the obtained resin composition does not necessarily contain themedium.

Various additives such as pigments, heat stabilizers, antioxidants,weathering agents, flame retardants, plasticizers, lubricants, releaseagents, antistatic agents and fillers may be added to the biodegradablepolyester resin composition of the present invention according to needwithin the range in which the properties of the composition are notsignificantly damaged. As such heat stabilizer and antioxidant, hinderedphenol, a phosphorus compound, hindered amine, a sulfur compound, acopper compound, halogenated alkali metal or a mixture thereof may beused. Examples of inorganic fillers include talc, calcium carbonate,zinc carbonate, wallastonite, silica, alumina, magnesium oxide, calciumsilicate, sodium aluminate, calcium aluminate, sodium aluminosilicate,magnesium silicate, glass balloon, carbon black, zinc oxide, antimonytrioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramicwhisker, potassium titanate, boron nitride, graphite, glass fiber andcarbon fiber. Examples of organic fillers include naturally occurringpolymers such as starch, cellulose fine particles, wood flour, bean curdrefuse, husk and bran, and modified products of these.

The method of adding the above-described additive or anotherthermoplastic resin to the biodegradable polyester resin composition ofthe present invention is not particularly limited. For example, afterusual melting by heating, materials may be kneaded by a conventionallyknown kneading method using a single screw extruder, a twin screwextruder, a roll mill or a Brabender mixer. In addition, using a staticmixer or a dynamic mixer together is also effective. The above-describedadditive or another thermoplastic resin may be added upon polymerizationof the biodegradable resin.

As the method of foaming for producing a foamed article from thebiodegradable polyester resin composition of the present invention, anyof the general methods may be used. For example, a decomposition-typefoaming agent that decomposes at the melting temperature of the resin ispreviously added to the resin using an extruder, and the resultant isextruded from a slit nozzle in the form of a sheet, or from a circularnozzle in the form of a strand. Examples of decomposition-type foamingagents include azo compounds which are typically azodicarbonamide andbarium azodicarboxylate, nitroso compounds which are typicallyN,N′-dinitrosopentamethylenetetramine, hydrazine compounds which aretypically 4,4′-oxybis(benzenesulfonylhydrazide) andhydrazo-dicarbonamide and inorganic foaming agents such as sodiumhydrogen carbonate. Foaming may also be performed by pouring a volatilefoaming agent from the middle of the extruder. Examples of foamingagents in this case include inorganic compounds such as nitrogen, carbondioxide and water, hydrocarbons such as methane, ethane and butane,fluorocarbon compounds and organic solvents which are typically alcoholssuch as ethanol and methanol. A method may also be used comprisingpreviously preparing fine particles of a resin composition, impregnatingthe above-described foaming agent into an organic solvent or water, andthen foaming by changing temperature or pressure, thereby preparingfoamed fine particles. Specific uses of the biodegradable foam sheets orfoam plates prepared by extrusion foaming include decorative sheets orvarious boards as they are, or they may be bended to be used as lunchboxes, decoration boxes or buffer materials, or subjected to drawing andused as food containers, trays, cups, gardening pots, interior materialsof automobiles, mannequins and toys. Foamed particles may be used asvarious buffer materials after molding, or directly as cushionmaterials.

Biodegradable foam sheets and foam plates prepared by extrusion foamingmay be subjected to deep draw forming such as vacuum forming,air-pressure forming or vacuum air-pressure forming to produce foodcontainers, farming and gardening containers, blister pack containersand press-through packages. The temperature for deep draw forming andheat treatment is preferably (Tg+20° C.) to (Tm−20° C.) . When the deepdraw forming temperature is lower than (Tg+20° C.), deep drawing may bedifficult and heat resistance of the obtained container may beinsufficient. When the deep draw forming temperature is higher than(Tm−20° C.), the thickness of molded articles tends to be uneven or theimpact resistance thereof may be decreased due to disorderedorientation.

The method of extrusion molding for producing an extrusion moldedarticle from the biodegradable polyester resin composition of thepresent invention will now be described. For extrusion molding, a T-diemethod or a cylindrical die method may be employed. The extrusionmolding temperature needs to be not lower than the melting point (Tm) orthe flow initiation temperature of the biodegradable polyester resincomposition, and is in the range of preferably 180 to 230° C., morepreferably 190 to 220° C. When the molding temperature is too low,molding may be unstable and overload may be easily caused. When themolding temperature is too high, the biodegradable polyester resin maybe decomposed and cause problems that the strength of the obtainedextrusion molded article is decreased and that the molded article iscolored, for example. While biodegradable sheets or pipes may beproduced by extrusion molding, in order to improve their heatresistance, heat treatment may be performed at not lower than the glasstransition temperature (Tg) of the biodegradable polyester resincomposition to not higher than (Tm−20° C.).

Specific uses of the biodegradable sheets or pipes produced by extrusionmolding include a master sheet for deep draw molding, a master sheet forbatch foaming, cards such as credit cards, plastic boards, plasticfolders, drinking straws and farming and gardening hard pipes. Further,biodegradable sheets may be subjected to deep draw forming such asvacuum forming, air-pressure forming or vacuum air-pressure forming toproduce food containers, farming and gardening containers, blister packcontainers and press-through packages. The temperature for deep drawforming and heat treatment is preferably (Tg+20° C.) to (Tm−20° C.).When the deep draw forming temperature is lower than (Tg+20° C.), deepdrawing may be difficult and heat resistance of the obtained containermaybe insufficient. When the deep draw forming temperature is higherthan (Tm−20° C.), the thickness of molded articles tends to be uneven orthe impact resistance thereof may be decreased due to disorderedorientation.

The form of food containers, farming and gardening containers, blisterpack containers and press-through packages is not particularly limited,but for storing food, goods and medicines, the material is deep-drawn toa depth of preferably not less than 2 mm. The thickness of the containeris not particularly limited, but in view of the strength of thecontainer, the container has a thickness of preferably not less than 50μm, more preferably 150 to 500 μm. Specific examples of food containersinclude fresh food trays, instant food containers, fast food containersand lunch boxes. Specific examples of farming and gardening containersinclude seedling pots. Examples of blister pack containers includepackaging containers of various products other than food such as officesupplies, toys and dry cells.

The method of blow molding for producing a blow-molded article from thebiodegradable polyester resin composition of the present invention willnow be described. For blow molding, direct blowing in which raw materialchips are directly molded, injection blow molding in which a preform(closed-end parison) is formed by injection molding followed by blowmolding, stretch blow molding, or the like may be employed.Alternatively, either of a hot parison method in which blow molding iscontinuously performed after forming a prefoam and a cold parison methodin which a prefoam is once cooled, taken out and then heated again toperform blow molding may be employed. The blow molding temperature needsto be (Tg+20° C.) to (Tm−20° C.) When the blow molding temperature islower than (Tg+20° C.), molding may be difficult and heat resistance ofthe obtained container may be insufficient. When the blow moldingtemperature is higher than (Tm−20° C.), problems may arise that thethickness of molded articles tends to be uneven and blowdown occurs dueto decrease in the viscosity, for example, and therefore thistemperature range is not preferable.

Regarding the method of injection molding for producing an injectionmolded article from the biodegradable polyester resin composition of thepresent invention, a general injection molding method may be used. Gasinjection molding, injection press molding, or the like may also beused. The cylinder temperature in injection molding needs to be notlower than Tm or the flow initiation temperature, and is in the range ofpreferably 180 to 230° C., more preferably 190 to 220° C. When themolding temperature is too low, molding may be unstable because ofoccurrence of short shot, and overload may be easily caused. When themolding temperature is too high, the biodegradable polyester resin maybe decomposed and cause problems that the strength of the obtainedextrusion molded article is decreased and that the molded article iscolored, for example, and therefore this temperature range is notpreferable. On the other hand, the mold temperature needs to be nothigher than (Tm−20° C.) . When crystallization is advanced within themold in order to improve the heat resistance of the biodegradablepolyester resin, the composition is preferably kept at (Tg+20° C.) to(Tm−20° C.) for a pre-determined time and cooled to the Tg or lower. Onthe other hand, in the case of post crystallization, the composition ispreferably directly cooled to the Tg or lower, and then heat treatedagain at the Tg to (Tm−20° C.).

In the case of injection molding of a foamed article, a resin and afoaming agent may be previously kneaded, or a foaming agent may beintroduced from the middle of the extruder to perform molding. In suchcase, a general molding method may be applied.

The form of injection molded articles produced by the above-describedinjection molding is not particularly limited, and specific examplesthereof include tableware such as dishes, bowls, pots, chopsticks,spoons, forks and knives, liquid containers, container caps, officesupplies such as rulers, pens and pencils, plastic folders and CD cases,commodities such as sink strainers, garbage cans, basins, toothbrushes,combs and hangers, farming and gardening materials such as flowerpotsand seedling pots, various toys such as plastic models, resin componentsfor electric appliances such as air conditioner panels, refrigeratortrays and various cases, and resin components for automobiles such asbumpers, instrument panels and door trims. The form of the liquidcontainer is not limited, but in order to hold liquid, the compositionmay be molded so that the container has a depth of preferably not lessthan 20 mm. The thickness of the container is not particularly limited,but in view of the strength of the container, the container has athickness of preferably not less than 0.1 mm, more preferably 0.1 to5mm. Specific examples of liquid containers include beverage cups andbottles for milk products, soft drinks and liquors, temporary storagecontainers of seasonings such as soy source, sauce, mayonnaise, ketchupand cooking oil, containers of shampoo and conditioner, containers ofcosmetics and containers of agricultural chemicals.

EXAMPLE

The present invention will now be described in detail based on Examples,but the present invention is not limited to these Examples. Themeasurement methods of property values in Examples and ComparativeExamples are as follows.

-   (1) Molecular weight (−): Measured using a gel permeation    chromatography (GPC) instrument equipped with a differential    refractometer (made by Shimadzu Corporation) eluting with    tetrahydrofuran at 40° C. and calculated based on standard    polystyrene.-   (2) Flexural modulus (GPa): In accordance with the method described    in ASTM-790, a test piece of 150 mm×10 mm×3 mm was prepared and load    was applied at a deformation rate of 1 mm/minute to measure the    flexural modulus.-   (3) Melting point (° C.) : Measured using a differential scanning    calorimeter DSC-7 (made by Perkin Elmer Inc.) at a temperature    increase rate of 10° C./minute, and the temperature at which a    melting endothermic curve has the extreme value is defined as the    melting point.-   (4) MFR (g/10 minutes): Measured in accordance with the method    described in JIS K7210 under the condition described in Attachment    A, Table 1-D.-   (5) Elongational viscosity (−): A test piece of 60 mm×7 mm×1 mm    (thickness) was prepared, and using an elongational viscosity    measuring instrument RME (made by Rheometric Scientific Inc.), both    ends of the test piece were held by a metal belt clamp, and the test    piece was rotated at a strain rate of 0.1 sec⁻¹ at a temperature    10° C. higher than the melting point of the resin composition to    apply elongational deformation thereto, and the torque applied to    the pinch roller during deformation was measured to determine the    elongational viscosity.-   (6) Modulus of strain hardening (a₂/a₁): As shown in FIG. 1, the    ratio (a₂/a₁) of a gradient a₁, in a linear region at an initial    stage of elongation before appearance of a bending point to a    gradient a₂ of a later stage of elongation after the bending point    was calculated from a double logarithmic plot of elongation time and    elongational viscosity. A test piece of 7 mm×60 mm×1 mm (thickness)    was used for the measurement. The melting temperature was set to    (the melting point of the resin +10° C.).-   (7) Crystallization rate index (minutes): Using a DSC instrument    (made by Perkin Elmer Inc., Pyrisl DSC), a sample was heated from    20° C. to 200° C. at a temperature increase rate of 500° C./minute    and kept at 200° C. for 5 minutes. Then, the temperature was    decreased from 200° C. to 130° C. at 500° C./minute and kept at    130° C. to allow crystallization. As shown in FIG. 2, the finally    reached crystallization degree is defined as 1 and the time at which    the crystallization degree has reached 0.5 was determined to be the    crystallization rate index (minutes).-   (8) Expansion ratio: The ratio of the density (D1) of a foamed    article obtained by dividing the mass of a foamed article by the    volume of the foamed article measured by immersing the article in    water to the true density of the resin (D0), which is an index of    lightweight and cushioning properties.    expansion ratio=D0/D1-   (9) Appearance of foamed article:-   good: uniform sheet, no roughness on the surface-   poor: non-uniform sheet, roughness due to broken bubbles found on    the surface-   (10) Molding cycle (second): Index of injection moldability;    injection molding was performed using an injection molding machine    (made by Toshiba Machine Co., Ltd., IS-100E) under conditions of a    molding temperature of 200° C. and a mold temperature of 110° C. to    form a release-type cup (diameter 38 mm, height 300 mm), and the    cycle time for the cup to be released in good condition was    measured.-   (11) Blow moldability: Using a blow molding machine (made by NISSEI    ASB MACHINE CO., LTD., ASB-50HT), a preform 30 mm in diameter, 100    mm in height and 3.5 mm in thickness was prepared at a molding    temperature of 200° C. The obtained preform was heated to a surface    temperature of 80° C. and blow-molded into a bottle-shaped mold (90    mm in diameter, 250 mm in height) to prepare a molded article 0.35    mm in thickness. The appearance of the obtained molded article was    evaluated as follows.-   good: excellent molded article as intended was obtained moderate:    could be molded almost as intended, but partially defective-   poor: could not be molded as intended-   (12) Operationability: Operationability for producing a    biodegradable polyester resin composition was evaluated as follows.-   good: operable for more than an hour without any trouble-   poor: serious troubles occurred such as frequent break of strand and    stopping of screw-   (13) Extrusion moldability: The biodegradable polyester resin    composition was extruded into a plate and the appearance of the    obtained molded article was evaluated as follows.-   good: molded article of desired shape without deflection was    obtained-   moderate: molded article was deflected-   poor: molded article of desired shape was not obtained-   (14) Oxygen permeability coefficient (ml·mm/m²·day·MPa): Resin    pellets were press-molded into a sheet of 300 μm in thickness using    a pressing machine, and the oxygen permeability coefficient was    measured using a differential pressure type gas permeability    measurement system (made by GTRTEC Corporation, GTR-30XAU) under    conditions of 20° C. and 90% RH. The oxygen permeability coefficient    was calculated by the following formula.    oxygen permeability coefficient (ml·mm/m²·day·MPa)=amount of oxygen    permeated (ml/m²·day·MPa)×thickness of sheet (mm)

The oxygen permeability coefficient is an index of gas barrierproperties, and the smaller the value, the better the gas barrierproperties.

The raw materials and secondary raw materials used in Examples andComparative Examples are listed below.

(1) Biodegradable Polyester Resin:

-   A: polylactic acid (weight average molecular weight: 140,000,-   L-type 99%, D-type 1%, melting point 168° C., MFRl1g/10minutes)-   B: polylactic acid (weight average molecular weight: 200,000,-   L-type 99%, D-type 1%, melting point 168° C., MFR 3 g/10 minutes)-   C: polylactic acid (weight average molecular weight: 150,000,-   L-type 96%, D-type 4%, melting point 112° C., MFR 10 g/10 minutes)-   D: polylactic acid resin (1,4-butanediol/succinic acid/lactic acid    copolymer, melting point 110° C., MFR 5 g/10 minutes)-   E: polybutylene succinate (melting point 115° C., MFR 30 g10    minutes)-   F: terephthalic acid/adipic acid/1,4-butanediol copolymer, melting    point 108° C., MFR 5 g/10 minutes    (2) (Meth)acrylic Acid Ester Compound:-   I: polyethylene glycol dimethacrylate (hereinafter    “PEGDM”)(available from NOF Corporation)-   II: trimethylpropane trimethacrylate (hereinafter “TMPTM”)    (available from NOF Corporation)-   III: polyethylene glycol diacrylate (hereinafter “PEGDA”)(available    from NOF Corporation)-   IV: glycidylmethacrylate (hereinafter “GM”)(available from NOF    Corporation)    (3) Layered Silicate:-   1. LUCENTITE SAN: swellable hectorite in which an interlayer ion is    substituted by a dimethyldioctadecylammonium ion (available from    CO-OP Chemical Co., Ltd., average particle size 0.1 μm).-   2. LUCENTITE SEN: swellable hectorite in which an interlayer ion is    substituted by a dihydroxyethyl methyldodecylammonium ion (available    from CO-OP Chemical Co., Ltd., average particle size 0.1 μm).-   3. S-BEN E: montmorillonite in which an interlayer ion is    substituted by a trimethyloctadecylammonium ion (available from    HOJUN Co., Ltd., average particle size 2.5 μm)-   4. Somasif MEE: swellable fluoromica in which an interlayer ion is    substituted by a dihydroxyethyl methyldodecylammonium ion (available    from CO-OP Chemical Co., Ltd., average particle size 6.3 μm)    (4) Peroxide:-   1. di-t-butyl peroxide (available from NOF Corporation)-   2. 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 (available from NOF    Corporation)-   3. powder of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 diluted    with inert solid (available from NOF Corporation), previously    dry-blended to the resin to be used

Examples 1 to 3

100 parts by mass of A: polylactic acid (weight average molecular weight140,000, L-type 99%, D-type 1%, melting point 168° C., MFR 11 g/10minutes) which is a biodegradable polyester resin, 4 parts by mass ofS-BEN E which is a layered silicate and 1.0 part by mass of fine talcpowder which is a nucleating agent (available from Hayashi Kasei Co.,Ltd., average particle size 2.5 μm) were dry-blended using a twin-screwkneading extruder (made by Ikegai Corporation, PCM-30, die diameter 4mm×3H, kneading temperature 200° C.), and supplied to the extrusionfeeder. PEGDM of I which is a (meth)acrylic acid ester compound was usedin a proportion shown in Table 1, and a mixed solution of the PEGDM,di-t-butyl peroxide which is liquid peroxide and acetyl tributyl citratewhich is a plasticizer was prepared so that the proportion thereof was1:2:5 parts by mass. The obtained mixed solution was supplied to themiddle part of the extruder using a liquid metering pump. Thedry-blended resin and the mixed solution described above weremelt-kneaded, extruded, pelletized and then dried to give abiodegradable polyester resin composition.

The biodegradable polyester resin composition and carbon dioxide gashaving a concentration of 1.0% by mass which is a foaming agent weresupplied to a twin screw foaming extruder (made by Ikegai CorporationPCM-30, die lips: 1.2 mm in width ×40mm in length) and a foam sheet wasprepared under conditions of a kneading temperature of 200° C. and a dietemperature of 160° C.

Properties of the resin compositions and the foamed articles obtainedare shown in Table 1. TABLE 1 Ex. 1 Ex. 2 Ex. 3 Com. Ex. 1 Com. Ex. 2biodegradable kind A A A A A polyester resin part(s) by mass 100 100 100100 100 (meth) acrylic kind I I I — I acid ester compound part(s) bymass 0.10 1.0 3.0 — 12 Layered silicate kind 3. 3. 3. 3. 3. part(s) bymass 4 4 4 4 4 operationability good good good good poor MFR g/10minutes 1.3 0.8 0.6 11.8 — crystallization minute 2 1.5 0.5 32 — rateindex modulus of strain 14 18 25 1.03 — hardening oxygen permeability ml· mm/m² · 140 152 140 155 — coefficient day · MPa flexural modulus GPa3.8 4.1 4 .3 3.0 — expansion ratio 5.1 8.0 10 — — (bubbles broken)appearance of good good good poor — foamed article sheet size: mm × mm 5× 42 7 × 44 8 × 48 1 × 40 — thickness × sheet width

In the resulting resin compositions of Examples 1 to 3, the (meth)acrylic acid ester compound and the layered silicate were mixed at aratio within the range of the present invention, and thus thecrystallization rate was high and the operationability was excellent.Further, the obtained biodegradable polyester resin composition had ahigh modulus of strain hardening and was excellent in flexural modulus.In addition, because the (meth)acrylic acid ester compound wasmelt-kneaded after mixing the layered silicate with the polyester resin,the obtained resin composition was excellent in operationability andmoldability. The foamed articles obtained using the biodegradablepolyester resin composition had closed cells, a uniform thickness andwere excellent in appearance.

Comparative Example 1

No (meth) acrylic acid ester compound was mixed thereto. Except forthat, a resin composition was prepared and a foam sheet was produced inthe same manner as in Example 1.

Properties of the resin composition and the foamed article obtained areshown in Table 1.

Comparative Example 2

The mixing ratio of the (meth)acrylic acid ester compound was set to 12parts by mass, which is beyond the range of the present invention.Although it was attempted to prepare a foam sheet in the same manner asin Example 1 except for the above, the resin composition was too viscousto be extruded, and a sheet was not obtained.

In Comparative Example 1, mechanical strengths, typically flexuralmodulus, were not improved and the obtained composition had a lowmodulus of strain hardening because no (meth)acrylic acid ester compoundwas contained. Further, when the resin composition was subjected tofoaming, bubbles were broken and the thickness of the foam sheet wasuneven.

In Comparative Example 2, the resin composition was too viscous asdescribed above to be steadily extruded and preparation of the resincomposition was unsuccessful, because the amount of the (meth)acrylicacid ester compound added was beyond the range of the present invention.

Examples 4 to 13

The kind and the mixing ratio of the biodegradable polyester resin andthe (meth)acrylic acid ester compound in Example 1 were changed asdescribed in Tables 2-1 and 2-2. Except for that, a biodegradablepolyester resin composition was prepared in the same manner as inExample 1.

The obtained biodegradable polyester resin composition and carbondioxide gas having a concentration of 1.0% by mass which is a foamingagent were supplied to a twin screw foaming extruder (made by IkegaiCorporation PCM-45, die lips: 0.7 mm in width×65 mm in length) and afoam sheet was prepared under conditions of a kneading temperature of200° C. and a die temperature of 160° C. Properties of the resincompositions and the foamed articles obtained are shown in Tables 2-1and 2-2. TABLE 2-1 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 biodegradable kind A AA B C polyester resin part(s) by mass 100 100 100 100 100 (meth) acrylickind III I IV I I acid ester compound part(s) by mass 0.10 0.10 0.100.10 0.10 Layered silicate kind 3. 3. 3. 3. 3. part(s) by mass 4 4 4 4 4operationability good good good good Good MFR g/10 minutes 1.2 1.3 0.91.0 1.1 crystallization minute 2 2 1.5 4 20 rate index modulus of strain15 14 17 13 12 hardening oxygen permeability ml · mm/m² · 160 155 153140 141 coefficient day · MPa flexural modulus GPa 4.1 4.0 4.1 4.3 4.0expansion ratio 7.5 7.3 7.6 7.2 7.0 appearance of good good good goodGood foamed article sheet size: mm × mm 5 × 70 5 × 68 6 × 71 5 × 67 5 ×65 thickness × sheet width

TABLE 2-2 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 biodegradable kind A/D A/EA/F A/E A/F polyester resin part(s) by mass 80/20 50/50 20/80 80/2080/20 (meth) acrylic kind I I I I I acid ester compound part(s) by mass0.10 0.10 0.10 0.10 0.10 Layered silicate kind 3. 3. 3. 3. 3. part(s) bymass 4 4 4 4 4 operationability good good good good good MFR g/10minutes 1.1 0.8 0. 6 0.9 0.8 crystallization minute 3.2 3.6 4.0 3.2 5.5rate index modulus of strain 8 10 13 5.0 4.5 hardening oxygenpermeability ml · mm/m² · 160 162 153 153 165 coefficient day · MPaflexural modulus GPa 3. 9 3.7 3.3 3.6 3.7 expansion ratio 7.0 7.5 8.15.2 4.3 appearance of good good good good good foamed article sheetsize: mm × mm 5 × 66 7 × 70 8 × 70 4 × 67 3 × 67 thickness × sheet width

In Examples 4 to 6, the kind of (meth)acrylic acid ester compound waschanged, and in Examples 7 to 13, the kind of biodegradable polyesterresin was changed. Since the mixing ratio of the biodegradable polyesterresin, the layered silicate and the (meth)acrylic acid ester compoundwas within the range of the present invention in all cases, thecompositions had a high crystallization rate, a high modulus of strainhardening, and were excellent in flexural modulus, and uniform foamedarticles having closed cells were obtained.

Examples 14 to 18

The kind and the mixing ratio of layered silicate are changed as shownin Table 3-1. Except for that, a biodegradable polyester resincomposition was prepared in the same manner as in Example 1.

The obtained biodegradable polyester resin composition and carbondioxide gas having a concentration of 1.0% by mass which is a foamingagent were supplied to a twin screw foaming extruder (made by IkegaiCorporation PCM-45, die lips: 0.7 mm in width×65 mm in length) and afoam sheet was prepared under conditions of a kneading temperature of200° C. and a die temperature of 160° C.

Properties of the resin compositions and the foamed articles obtainedare shown in Table 3-1. TABLE 3-1 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18biodegradable kind A A A A A polyester resin part(s) by mass 100 100 100100 100 (meth) acrylic kind I I I I I acid ester compound part(s) bymass 0.10 0. 10 0.10 0.10 0.10 Layered silicate kind 1. 2. 4. 4. 4.part(s) by mass 4 4 4 2 8 operationability good good good good good MFRg/10 minutes 0.5 1.3 0.9 1.3 0.6 crystallization minute 2 3 0.5 3 0.5rate index modulus of strain 1.8 2.5 18 10.2 22 hardening flexuralmodulus GPa 4.0 4.0 4.2 3.9 4.5 Oxygen permeability ml · mm/m² · 170 17285 120 60 coefficient day · MPa expansion ratio 5.6 6.0 7.9 8.0 4.6Appearance of good good good good good foamed article sheet size: mm ×mm 4 × 66 4 × 68 5 × 70 5 × 72 3 × 67 thickness × sheet width

In Examples 14 to 16, the kind of layered silicate was changed, and inExamples 17and 18, the amount of layered silicate was changed. Since themixing ratio of the biodegradable polyester resin, the layered silicateand the (meth)acrylic acid ester compound was within the range of thepresent invention in all cases, the compositions had a highcrystallization rate, a high modulus of strain hardening and wasexcellent in flexural modulus, and uniform foamed articles having closedcells were obtained. Further, as demonstrated in Example 16, whenSomasif MEE was used as the layered silicate, gas barrier propertieswere particularly improved. In addition, as demonstrated in Examples 16to 18, the more the amount of the layered silicate added, the more thegas barrier properties are improved.

Comparative Example 3

Somasif MEE was used as a layered silicate, and the mixing ratio thereofwas set to 0.03 part by mass which is below the range of the presentinvention. Except for that, a resin composition was prepared and a foamsheet was produced in the same manner as in Example 1.

Properties of the resin composition and the foamed article obtained areshown in Tables 3-2.

Comparative Example 4

Somasif MEE was used as a layered silicate, and the mixing ratio thereofwas set to 22 parts by mass which is beyond the range of the presentinvention. Although it was attempted to prepare a foam sheet in the samemanner as in Example 1 except for the above, the viscosity of the resincomposition was too low and the resin composition could not be extrudedor formed into a sheet.

In Comparative Example 3, because the content of the layered silicatewas too low, the oxygen permeability coefficient was increased and themodulus of strain hardening was decreased, and the mechanical strengthwas thus not improved.

In Comparative Example 4, because the content of the layered silicatewas too high, the viscosity was insufficient and the gas barrierproperties were degraded. Further, bubbles were broken and a foam sheethaving a uniform thickness was not obtained as described above. TABLE3-2 Com. Ex. Com. Ex. 3 4 biodegradable kind A A polyester resin part(s)by mass 100 100 (meth) acrylic kind I I acid ester part(s) by mass 0.100.10 compound Layered silicate kind 4. 4. part(s) by mass 0.03 22operationability good good MFR g/10 minutes 1.4 2.5 crystallizationminute 0.2 4.6 rate index modulus of strain 0.4 12 hardening flexuralmodulus GPa 3.2 4.4 oxygen ml · mm/m² · 190 70 permeability day · MPacoefficient expansion ratio 3.5 — (bubbles broken) appearance of goodpoor foamed article sheet size: Mm × mm 3 × 65 — thickness × sheet width

Example 19

100 parts by mass of A: polylactic acid (weight average molecular weight140,000, L-type 99%, D-type 1%, melting point 168° C., MFR 11 g/10minutes) which is a biodegradable polyester resin, 4 parts by mass ofSomasif MEE which is a layered silicate, 1.5 parts by mass of fine talcpowder having an average particle size of 1.0 μm (available from NIPPONTALC CO.,LTD.) which is a nucleating agent, and 1.0% by mass, based onthe resin component, of powder of2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 diluted with inert solidwhich is a peroxide were dry-blended using the twin-screw kneadingextruder used in Example 1, and supplied to the extrusion feeder.Subsequently, a mixed solution of 0.1 part by mass of PEGDM which is a(meth)acrylic acid ester compound and acetyl tributyl citrate which is aplasticizer was prepared so that the proportion thereof was 1:5 parts bymass. The obtained mixed solution was supplied to the middle part of theextruder using a liquid metering pump. The dry-blended resin and themixed solution were melt-kneaded, extruded, pelletized and then dried togive a biodegradable polyester resin composition.

The obtained biodegradable polyester resin composition was introducedinto a batch foaming machine (made by Taiatsu Techno Corporation,autoclave 500 ml). The composition was set temperature to 150° C. andthe carbon dioxide gas injection pressure was set to 15 MPa, and after60 minutes of carbon dioxide gas injection, the pressure was released atonce to prepare a carbon dioxide gas batch foamed article.

Properties of the resin composition and the foamed article obtained areshown in Table 4. TABLE 4 Ex. 19 Ex. 20 biodegradable kind A A polyesterresin part(s) by mass 100 100 (meth) acrylic kind I I acid estercompound part(s) by mass 0.10 0.10 layered silicate kind 4. 4. part(s)by mass 4 4 operationability good good MFR g/10 minutes 0.9 0.9crystallization rate index minute 0.5 0.5 modulus of strain hardening 1818 flexural modulus GPa 4.2 4.2 expansion ratio 34 54 appearance offoamed article good good

Example 20

Butane gas was used as a foaming agent instead of carbon dioxide gas.Except for that, a batch foamed article was prepared in the same manneras in Example 19.

Properties of the resin composition and the foamed article obtained areshown in Table 4.

In Example 19, the composition had a high crystallization rate and ahigh modulus of strain hardening because the viscosity increasing effectby the (meth)acrylic acid ester compound was high, and a foamed articlehaving closed cells with a high expansion ratio was obtained.

In Example 20, the butane gas used as the foaming agent had a highsolubility in the resin, and thus a foamed article having closed cellswith a high expansion ratio was obtained.

Example 21

The biodegradable polyester resin composition obtained in Example 19 wasmelt-kneaded at a melting temperature of 210° C. using a foam sheetproduction machine of twin screw kneader type (made by TOSHIBA MACHINECO. LTD. TEM48BS type, die lip distance: 0.3 mm, circular die outputdiameter: 160 mmφ). A sheet was prepared under conditions of a coolingzone temperature of 140° C., a die temperature of 160° C., a carbondioxide gas concentration of 2.0%, a discharge amount of 50 Kg/h bytwo-shot molding of a sheet width of 640 mm×2 at a take up rate of 1.5m/minute.

The obtained foam sheet had a thickness of 2.0 mm, was uniform and hadclosed cells with an expansion ratio of 7.5 times. The foam sheet had aflexural modulus of 4.4 Gpa, which was excellent in mechanical strength.

A food tray (drawing ratio of container (L/D): 1:5) was prepared fromthe foam sheet using a thermoforming machine (made by Asano LaboratoriesCo., Ltd.) with a mold for lid-container integral molding. Specifically,the sheet temperature was set to 130° C., and after heating for 10seconds, the sheet was transferred to the mold and subjected to vacuummolding for 5 seconds at a mold temperature of 110° C. to prepare amolded article.

The obtained molded article had no molding flaw and was a uniformlyfoamed food tray. The expansion ratio of the tray was 7.3 times whichwas the same as the expansion ratio of the sheet before molding.

Further, an appropriate amount of water was poured on the tray and thetray was treated in a microwave oven (output 500 W) for 3 minutes. As aresult, there was little deformation or contraction in the tray aftertreatment.

Examples 22 and 23

Using the biodegradable polyester resin composition obtained in Example2 in Example 22, and the biodegradable polyester resin compositionobtained in Example 19 in Example 23, injection molding was performedwith an injection molding machine (made by TOSHIBA MACHINE CO. LTD.,IS-100E) to form a release-type cup (diameter 38 mm, height 300 mm). Thecycle time for the cup to be released was measured at a moldingtemperature of 200° C. and a mold temperature of 110° C.

The obtained measurement results are shown in Table 5. TABLE 5 Ex. Ex.Com. Com. Com. 22 23 Ex. 5 Ex. 6 Ex. 7 biodegradable kind A A A A Apolyester resin part(s) 100 100 100 100 100 by mass (meth) acrylic kindI I — I — acid ester part(s) 1.0 0.10 — 0.10 — compound by mass layeredsilicate kind 3. 4. 3. 4. — part(s) 4 4 4 0.03 — by massoperationability good good good Good — MFR g/10 1.3 0.9 11.8 1.4 11minutes crystallization minute 2 0.5 32 0.2 110 rate index modulus ofstrain 14 18 1.03 0.4 — hardening molding cycle second 45 40 120 55 600or more

In examples22and23, the crystallization rate was improved and themolding cycle time was shortened due to the synergistic effect of thelayered silicate and the (meth)acrylic acid compound.

Comparative Examples 5 and 6

In Comparative Example 5, the biodegradable polyester resin compositionobtained in Comparative Example 1 was used, and in Comparative Example6, the biodegradable polyester resin composition obtained in ComparativeExample3was used. Except for that, injection molding was performed inthe same manner as in Example 22, and the cycle time taken for the cupto be released was measured.

The obtained measurement results are shown in Table 5.

Comparative Example 7

The biodegradable polyester used in Example 1 alone was used withoutmixing the (meth)acrylic acid ester compound or the layered silicate.Injection molding was to be performed in the same manner as in Example22 except for the above, but was impossible because the operationabilitywas poor.

In Comparative Example 5, because no (meth)acrylic acid ester compoundwas mixed, the crystallization rate was extremely low and the moldingcycle was greatly lowered.

In Comparative Example 6, because the mixing ratio of the layeredsilicate was too small, the rigidity at higher temperature of thecomposition was insufficient and there was a problem with removal of themolded article, and this lowered operationability of injection molding.

In Comparative Example 7, because no (meth) acrylic acid ester compoundor a layered silicate was mixed, the composition had no strain hardeningproperty and had a low crystallization rate, and the operation wascompletely impossible as described above.

Examples 24 and 25

Using the biodegradable polyester resin composition obtained in Example2 in Example 24, and the biodegradable polyester resin compositionobtained in Example 19 in Example 25, preform 30 mm in diameter, 100 mmin height and 3.5 mm in thickness was prepared by a blow molding machine(made by NISSEI ASB MACHINE CO., LTD., ASB-50HT) under a condition of amolding temperature of 200° C. Then, the obtained preform was heated sothat the surface temperature was 80° C. and blow-molded into abottle-shaped mold (diameter 90 mm, height 250 mm) to obtain a moldedarticle 0.35 mm in thickness.

The obtained measurement results are shown in Table 6. TABLE 6 Ex. Ex.Com. Com. Com. 24 25 Ex. 8 Ex. 9 Ex. 10 biodegradable kind A A A A Apolyester part(s) 100 100 100 100 100 resin by mass (meth) acrylic kindI I — I — acid ester part(s) 1.0 0.10 — 0.10 — compound by mass layeredkind 3. 4. 3. 4. — silicate part(s) 4 4 4 0.03 — by mass operation- goodgood good Good — ability MFR g/10 1.3 0.9 11.8 1.4 11 minutecrystalliza- minute 2 0.5 32 0.2 110 tion rate index modulus of 14 181.03 0.4 — strain hardening blow good good moderate moderate poormoldability

In Examples 24 and 25, the crystallization rate was high and the blowmoldability was excellent due to the synergistic effect of the layeredsilicate and the (meth)acrylic acid ester compound.

Comparative Examples 8 and 9

In Comparative Example 8, the biodegradable polyester resin compositionobtained in Comparative Example 1 was used and in Comparative Example 9,the biodegradable polyester resin composition obtained in ComparativeExample3was used. Except for that, blow molding was performed in thesame manner as in Example 24.

The obtained measurement results are shown in Table 6.

Comparative Example 10

The biodegradable polyester used in Example 1 alone was used withoutmixing the (meth)acrylic acid ester compound or the layered silicate.Blow molding was to be performed in the same manner as in Example 24except for the above, but was impossible because the operationabilitywas poor.

In Comparative Example 8, because no (meth)acrylic acid ester compoundwas mixed, only a composition having a high MFR and low crystallizationrate was obtained, and the blow moldability was poor. Further, theobtained molded article was defective.

In Comparative Example 9, because the mixing ratio of the layeredsilicate was too small, the rigidity at higher temperature of thecomposition was insufficient and there was a problem with removal of themolded article, for example and this lowered operationability. And theobtained molded article was partially defective.

In Comparative Example 10, because no (meth)acrylic acid ester compoundor a layered silicate was mixed, the composition had no strain hardeningproperty and had a low crystallization rate, and blow molding wascompletely impossible as described above. Thus, the intended moldedarticle could not be obtained.

Examples 26 and 27

Using the biodegradable polyester resin composition obtained in Example2 in Example 26, and the biodegradable polyester resin compositionobtained in Example 19 in Example 27, a molded plate 50 mm in width and2.0 mm in thickness was prepared by an extrusion molding machine (madeby Ikegai Corporation, PCM-30) under a condition of a moldingtemperature of 210° C.

The obtained measurement results are shown in Table 7. TABLE 7 Ex. 26Ex. 27 Com. Ex. 11 Com. Ex. 12 Com. Ex. 13 biodegradable kind A A A A Apolyester resin part(s) by mass 100 100 100 100 100 (meth) acrylic kindI I — I — acid ester part(s) by mass 1.0 0. 10 — 0.10 — compound layeredkind 3. 4. 3. 4. — silicate part(s) by mass 4 4 4 0.03 —Operationability good good good Good — MFR g/10 minute 1.3 0.9 11.8 1.411 crystallization minute 2 0.5 32 0.2 110 rate index modulus of strain14 18 1.03 0.4 — hardening extrusion good good moderate moderate poormoldability

In Examples 26 and 27, the crystallization rate was high and theextrusion moldability was excellent due to the synergistic effect of thelayered silicate and the (meth)acrylic acid ester compound.

Comparative Examples 11 and 12

In Comparative Example 11, the biodegradable polyester resin compositionobtained in Comparative Example 1 was used, and in Comparative Example12, the biodegradable polyester resin composition obtained inComparative Example 3 was used.

Except for that, extrusion molding was preformed in the same manner asin Example 26.

The obtained measurement results are shown in Table 7.

Comparative Example 13

The biodegradable polyester used in Example 1 alone was used withoutmixing the (meth)acrylic acid ester compound or the layered silicate.Extrusion molding was to be performed in the same manner as in Example26 except for the above but was impossible because the operation abilitywas poor.

In Comparative Example 11, because no (meth)acrylic acid ester compoundwas mixed, the obtained composition had a high MFR, a lowcrystallization rate and poor extrusion moldability, and the obtainedplate was deflected.

In Comparative Example 12, because the mixing ratio of the layeredsilicate was too small, the rigidity at higher temperature of thecompound was insufficient to cause deflection of the plate, meaning thata molded article of the desired shape was not obtained.

In Comparative Example 13, because no (meth) acrylic acid ester compoundor layered silicate was mixed, the composition had no strain hardeningproperty and had a low crystallization rate, and extrusion molding wascompletely impossible as described above. Thus, the intended moldedarticle could not be obtained.

1. A biodegradable polyester resin composition comprising 100 parts bymass of a biodegradable polyester resin containing not less than 50% bymole of an α- and/or β-hydroxycarboxylic acid unit, 0.01 to 10 parts bymass of a (meth)acrylic acid ester compound and 0.05 to 20 parts by massof a layered silicate.
 2. The biodegradable polyester resin compositionaccording to claim 1, wherein a crystallization rate index is not morethan 30 (minutes).
 3. The biodegradable polyester resin compositionaccording to claim 1, wherein the (meth)acrylic acid ester compoundcontains at least two (meth)acrylic groups or at least one (meth)acrylicgroup and at least one glycidyl group or vinyl group.
 4. Thebiodegradable polyester resin composition according to claim 1, whereinthe α- and/or β-hydroxycarboxylic acid unit is D-lactic acid, L-lacticacid or a mixture thereof.
 5. The biodegradable polyester resincomposition according to claim 1, wherein, in a time-elongationalviscosity curve obtained by measuring elongational viscosity of thebiodegradable polyester resin composition at a temperature 10° C. higherthan the melting point of the biodegradable polyester resin composition,a ratio of a gradient a₁ in a linear region at an initial stage ofelongation before appearance of a bending point to a gradient a₂ of alater stage of elongation after the bending point (modulus of strainhardening =a₂/a₁) is 1.05 to less than
 50. 6. A process for producing abiodegradable polyester resin composition according to claim 1, whereinsaid process comprises melt-kneading a layered silicate with abiodegradable polyester, resin and then melt-kneading a (meth)acrylicacid ester compound and a peroxide therewith.
 7. A process for producinga biodegradable polyester resin composition according to claim 1,wherein said process comprises melt-kneading a layered silicate with abiodegradable polyester resin and then pouring a solution or adispersion of a (meth)acrylic acid ester compound thereinto, followed bymelt-kneading.
 8. A process for producing a biodegradable polyesterresin composition according to claim 1, wherein said process comprisesmelt-kneading a layered silicate with a biodegradable polyester-resinand then pouring a solution or a dispersion of a (meth)acrylic acidester compound and a peroxide, followed by melt-kneading.
 9. Abiodegradable resin foamed article obtained by foam molding of abiodegradable polyester resin composition according to claim
 1. 10. Abiodegradable resin molded article obtained by any of injection molding,extrusion molding and blow molding of a biodegradable polyester resincomposition according to claim 1.